This invention relates to a method of controlling clutch means for controlling the amount (degree) of power transmitted to wheels from an engine through a transmission and a method of determining the completion of clutch engagement.
This invention also relates to a method of controlling clutch opening for a constant power transmission and for bringing the vehicle into a creep state, when a transmission is in a running range and a throttle opening is below a given value.
So far there have been various types of clutch means such as the friction clutch plate type etc. used in connection with vehicle transmission.
To cite an example, in a clutch device disclosed in Japanese Patent (laid-open) publication No. 56(1981)-95722, a bypass line is provided between two hydraulic lines forming a closed circuit in a transmission with a hydraulic pump and a hydraulic motor, and a clutch valve is disposed in the bypass line to adjust the opening thereof. The controller for controlling the operation of the clutch valve is provided along with a first detection means for detecting engine speed and a second detection means for detecting throttle opening. The controller is so constructed as to deliver a control force proportional to engine speed to move the aforesaid clutch valve in a closing direction, and another control force proportional to throttle opening to move the aforesaid clutch valve in an opening direction.
In other words, in the aforesaid clutch device, a reference engine speed is set in correspondence to the throttle opening, and the clutch opening is controlled so that the actual engine speed agrees with the reference engine speed.
In this connection, to prevent an unnecessary or excessive increase in engine speed accompanying an increase in engine power in the vehicle start, it is necessary to timely select and properly control the opening of the bypass line, (the opening of the clutch valve) to have an appropriate initial load on the engine while the engine is idling. When the accelerator pedal is abruptly depressed to start the vehicle, the increase signal of throttle opening according to the depression of the accelerator pedal can be promptly inputted to the controller. But an increase in engine speed following the opening of the throttle valve is slightly delayed, and therefore the increase signal of engine speed is inputted to the controller with a slight time delay. Therefore, there may occur an instance when the engine speed is not fully imposed on the controller although the throttle opening is wide and a reference engine speed is high. Then a control action will be initiated corresponding to this condition to enlarge the opening of the bypass line, (to move clutch opening in the open direction. This may result in the engine speed unnecessarily increasing and exceeding the reference engine speed since the load on the engine is very low. Moreover, that excessive engine speed then is inputted to the controller, the clutch valve is rapidly actuated in the closing direction, thus failing to obtain a proper partial clutch engaged state, causing hunting or other jerky starting of the vehicle.